Conventionally there have been proposed a large number of structures for efficiently cooling semiconductor elements in semiconductor modules. For example, the Japan Institute of Invention and Innovation discloses in its published Technology Report No. 2003-504490 a structure having a heat sink immersed in a coolant liquid or similar fluid to cool a power device. This power device includes a power device and a heat sink arranged at opposite surfaces of the power device and immersed in a coolant fluid.
This power device has the heat sink formed in a recessed, curve surface with a plurality of protrusions thereon to have an increased surface area to cool the power device, and also pass the coolant turbulently to more efficiently cool the power device.
Japanese Patent Laying-Open No. 7-189684 discloses a heat exchange device having radiating fins arranged at a density varied in accordance with how air blown by a fan for cooling distributes in flow rate. This heat exchange device has the radiating fins spaced closer for a high-rate air flow area of a radiator and farther away for a low-rate air flow area of the radiator. This allows the radiator to thereacross have a substantially uniform amount of air passing therethrough to achieve an increased heat exchange rate.
As disclosed in Technology Report No. 2003-504490, however, the structure is intended to more effectively cool the entirety of the power device. It is not intended to enable the power device to have a uniform temperature profile.
In general, a power device is higher in temperature at the center than the periphery. Accordingly, how the device increases in temperature at the center is considered in limiting in amount an electric current passed to the power device. As such, power devices higher in temperature at the center than the periphery cannot exhibit their capabilities sufficiently.
In other words, to allow a power device to sufficiently exhibit its performance, it is important to cool the power device more efficiently and as uniformly as possible.
Furthermore, if the power device does not have a uniform temperature profile, the power device's interior, a material bonding the power device and an electrode together, and the like have stress caused therein and helping them to deteriorate. Japanese Patent Laying-Open No. 7-189684 and Technology Report No. 2003-504490 fail to consider such disadvantage.